Fernandez Lobbe, who put in a man-of-the-match performance, said the victory was reward for hard work by an emerging team.
"This is a great win for us. We have been searching for this win for a long time as a group," he told BBC1.
"The most important thing for us was to try to get that first win. We are happy to do it against such a good team."
Halfpenny extended Wales' lead with a fourth penalty early in the second half, but a penalty and drop goal from Sanchez, plus converted tries for wings Juan Imhoff and Gonzalo Camacho saw the visitors secure their second win over Wales in Cardiff, 11 years to the day after their first.